题目内容：

Half the world’s population could face a food crisis (危机) by 2100 due to climate change, a new report by US scientists warns. Rapid warming is likely to reduce crop yields in the tropics  (热带地区)  and subtropics (亚热带地区), according to Prof David Battisti of the University of Washington.

The most extreme summers of the last century will become common, he calculates, using 23 climate models. “We must urgently create crops that can bear heat and drought if we are to adapt in time，” he writes in Science Journal.

“The stresses on global food production from temperature alone are going to be huge，” said Mr Battisti. “And that doesn’t take into account water supplies stressed by the higher temperatures.”

He worked with Prof Rosamond Naylor on Food Security and the Environment, to examine the impact of climate change on the world’s food security. They predict there is greater than 90% probability that by 2100, the average growing­season temperatures in the tropics and subtropics will be higher than any temperatures recorded there to date.

“We are taking the worst of what we’ve seen historically and saying that in the future it is going to be a lot worse unless there is some kind of adaptation，” said Prof Naylor. “This is a powerful reason for us to invest in adaptation, because it is clear that  this  is the direction we are going in terms of temperature and it will take decades to develop new food crop varieties that can better bear a warmer climate.”

In the tropics,  the higher temperatures could be expected to cut yields of the primary food crops by 20%－40%, the researchers said. Rising temperatures also are likely to reduce soil moisture (湿度), cutting yields even further.

Currently three billion people live in the tropics and subtropics, and their number is expected nearly to double by the end of the century.

“You are talking about hundreds of millions of additional people looking for food because they won’t be able to find it where they find it now，” said Prof Battisti.

Crop failures would not be limited to the tropics, the scientists concluded.

1.The passage intends to tell us ________.

A. our world is becoming warmer

B. the consequences of global warming

C. the high temperatures may cause food crisis

D. the ways to adapt to the high temperatures

2.According to the passage, as a result of the high temperatures, ________.

a．crops will grow more quickly

b．water supplies will be stressed

c．soil moisture will be reduced

d．more food will be consumed

A. a  b    B. a  c

C. b  c    D. c d

3.We can draw the following conclusions EXCEPT that ________.

A. more people will live in the tropics

B. temperatures in the tropics will be higher

C. crop failures won’t be limited to the tropics

D. new food crop varieties will be developed soon